Dave Winer deleted his Dropbox account due to the ToS changes, and notes this in his post on the subject:

To people who say I over-reacted. How could you possibly know?

I am in the camp that thinks Winer over-reacted, but he is right that I don’t know yet if he did. What I do know is that the challenges that face the privacy and security concerns with Dropbox are the same that all other cloud services face — including Apple’s coming iCloud service and their past MobileMe services.

When deciding whether to use a service like Dropbox you have to make two decisions before you use it:

You must decide that the company you are going to use (in this case Dropbox) is not “evil”.

You must know that anything and everything you store online could be seen by others, and use the service accordingly.

If the changes bug you, then delete your account. If you just want to sync some encrypted data (that you encrypted) or some silly text files then use the service knowing that this data is not 100% private.

I don’t agree with the take Winer has on the ToS, I think they are OK and within the bounds of what the law requires of them — I am not, however, an attorney.